The present invention is an improvement, and method of using that improvement, to a family of belt-using, variable power transmission systems. Such systems include an endless belt power transmission system using pulleys, such as cone or tapered-face pulleys, with belt receiving surfaces formed by drive faces on axially movable, coaxially confronting members. Generally, such transmissions are called continuously variable transmissions, which will be referred to herein by the common abbreviation of xe2x80x9cCVT.xe2x80x9d More particularly, the variable power transmission systems using the improvement of the present invention axially move the confronting pulley surfaces in response to the centrifugal force produced by the rotational speed acting on a pivoted weight. The pivoted weight is a cam commonly called, and herein called, a camweight or a flyweight. The improvements of the present invention include improvements to the means of producing the centrifugal force so as to produce a more desirable side force on the belt as the shift ratio changes. The utility of the present invention extends to flyweight actuated devices not using belts.
As used herein, xe2x80x9cflyweightxe2x80x9d and xe2x80x9ccamweightxe2x80x9d are interchangeable.
A xe2x80x9cconventional flyweightxe2x80x9d consists of a symmetrical head surrounding a pivot axis (with a center) and one arm extending therefrom where the arm has a cam surface that, in operation, engages a roller or the like. The arm is sometimes described as being cantilevered. FIGS. 1A and 1B show examples of conventional flyweights. Characteristically, the head of a conventional flyweight, and its immediate vicinity, consists of an essentially symmetrical mass distribution radially from the center of the pivot axis. One manifestation of such symmetry would be an essentially constant radius from the center of the pivot to the outer edge of the head over approximately a semi-circle. Another manifestation of such symmetry would be the existence of an axis of symmetry extending essentially along the arm through the center of the pivot such that the distance to the outer edge of the head is approximately equal along pairs of radial lines emanating from the center of the pivot that have equal inclinations (angle) to the axis of symmetry.
A Ski-Doo type conventional flyweight is shown on FIG. 1C. The Ski-Doo type conventional flyweight interchanges the cam surface and roller placing the roller on the arm and fixing the cam surface.
xe2x80x9cCenter-of-mass,xe2x80x9d abbreviated herein as COM, is the centroid of the mass referred to. All masses have a COM. Because most of the mass of a conventional flyweight is contained in the arm and because of the symmetry of the head, the arm""s COM is close to the COM of the entire conventional flyweight.
The xe2x80x9creference linexe2x80x9d is the line that is normal to the rotational axis (which is usually the crankshaft center-line) and passes through the center of the pivot of the flyweight being discussed. xe2x80x9cShift ratioxe2x80x9d is the ratio of the diameter of the belt passing over the secondary pulley to the diameter of the belt passing over the primary pulley. Shift ratio is also the ratio of the angular velocity of the primary pulley to the angular velocity of the secondary pulley when there is no slippage. Typically, shift ratios vary from about 3:1 (at low vehicle speed) to 0.8:1.
The xe2x80x9cplumb linexe2x80x9d of a flyweight is, as the name suggests, a plumb line dropped from the center of the pivot of a conventional flyweight that is statically suspended by the pivot while free to rotate about the pivot. It extends in both directions from the center of the pivot and is essentially the same as a line passing through the center of the pivot and the arm""s COM. Note that the experimental method of determining the plumb line (just described) is only applicable to a conventional flyweight or a flyweight absent the mass supplements of the present invention. A flyweight according to the present invention shall have its plumb line determined after the removal of the mass concentrations of the present invention. Angles measured from the plumb line start at zero degrees for directions along the plumb line in the direction of the arm and increase in the direction of the cam surface on the arm. The shoulder of the preferred embodiment is preferably placed, integrally formed, or attached to a conventional flyweight so that the COM of the shoulder is within a 60 degree wide sector centered on the pivot""s center and extending from 60 degrees from the plumb line to 120 degrees from the plumb line.
xe2x80x9cQuadrants,xe2x80x9d in a plane normal to the pivot""s axis, are numbered from one to four increasing counterclockwise from a line segment that is normal to the plumb line and that extends from the pivot center on the side of the flyweight having the cam surface. Counterclockwise is a rotation from the line segment towards the head and clockwise is a rotation from the line segment towards the arm. It follows from the definitions that quadrant 1 encompasses 90 degrees from the plumb line to 180 degrees from the plumb line, that quadrant 2 encompasses 180 degrees from the plumb line to 270 degrees from the plumb line, that quadrant 3 encompasses from 270 degrees from the plumb line to zero degrees from the plumb line, and that quadrant 4 encompasses from zero degrees from the plumb line to 90 degrees from the plumb line. See FIG. 4. For a conventional flyweight, most of the arm and the arm""s cam surface are in the fourth quadrant.
Other definitions appear herein.
A conventional CVT has two tapered-faced pulleys interconnected with a belt of essentially fixed length. The sheaves of each pulley are able, under control, to move axially. One pulley""s shaft is usually connected to the crankshaft of the engine. The system including a pulley, and its ancillary parts, that is connected to the engine is called the driving, driver, or primary clutch. The other pulley is connected through a linkage to the vehicle""s drive train. It, and its ancillary parts, is called the driven or secondary clutch. Of necessity, when the sheaves of either pulley are close together, the associated belt must be located at a relatively large radius (distant from the axis of rotation) and when the sheaves of a pulley are far apart the associated belt must be located at a relatively small radius. It is also apparent that in a well designed system, because of the essentially fixed length of the belt, when the sheaves of one pulley are far apart then the sheaves of the other pulley must be close together. Larger shift ratios, characteristic of slower vehicle speeds, occur when the sheaves of the primary pulley are far apart and the sheaves of the secondary pulley are close together (rotational speed of the primary pulley is greater than the rotational speed of the secondary pulley). Smaller shift ratios, characteristic of high vehicle speed, occur when the sheaves of the primary pulley are close together and the sheaves of the secondary pulley are far apart (rotational speed of the primary pulley is less than the rotational speed of the secondary pulley).
Some of the ancillary parts of the primary clutch include a compression spring, or the like, tending to push the sheaves apart such that, at rest, the sheaves of the primary pulley have opened to allow the belt to lie close to the pulley""s rotational axis, effecting a large shift ratio. Such a belt position at rest results in the engine having a desirable minimal load when starting. The force produced by this spring increases as the sheaves of the primary pulley get closer together (lower shift ratios) and further compress the spring. Additional ancillary parts of the primary clutch include a set of pivoting flyweights on the primary clutch pushing on a roller, or the like, linked such that the sheave spacing, and thus shift ratio, is responsive to speed and torque needs of the secondary clutch. In the known CVT systems, the net result of the spring and flyweights of the primary clutch includes:
enough primary pulley belt side force to allow the engine to start and promptly to get up to approximately a rotational speed where the engine can deliver maximum power to its shaft;
a belt side force that increases with increasing vehicle speed (decreasing shift ratio) to a peak; and
a belt side force that then decreases with increasing vehicle speed.
The undesirable result of the just described belt side force is a tendency to lose power because of belt slippage due to insufficient belt side force while the vehicle is accelerating to near maximum speed. The desirable result of the just described belt side force is a tendency for the system, in the vicinity of maximum vehicle speed, to increase the shift ratio (deliver more torque) when the vehicle slows down. The present invention substantially cures the undesirable characteristic of a conventional system while leaving unchanged the desirable characteristic.
The typical role of the engine is to start, to accelerate promptly to a high rotational speed where the engine can deliver approximately its maximum power, and to remain at that high speed delivering approximately a constant amount of power. Power, in this context, is the product of torque and rotational velocity. The role of the CVT is to apportion the power delivered by the engine into a torque and speed portion depending on the vehicle""s speed. When the vehicle is moving slowly, the CVT has a high shift ratio, and the torque factor is relatively large. When the vehicle is moving rapidly, the CVT has a smaller shift ratio, and the torque factor is smaller.
Prior art improvements to flyweights appear to be mostly directed to enhancing performance of CVTs in the neighborhood of maximum vehicle speed, which is expected to be in the vicinity of shift ratios of 0.8:1. In other words, improvements have tended to improve high speed performance. Patents have been directed to improving the shape of flyweights, the distance from the center of rotation of the flyweight and its center-of-mass (COM) located along the flyweight""s arm, and the means of supporting the flyweights. Several recent patents have addressed the adjustability of conventional flyweights (i.e. being able to change the mass and COM of the arm of the flyweight without replacing the entire flyweight). U.S. Pat. Nos. 5,562,555 and 5,692,982 to Peterson effect adjustability by changing masses attached to multiple holes extending axially through the arm or by removing part of the arm most distant from the center of rotation while the flyweight is pivotally mounted to the driving clutch. (Axially means essentially parallel to the flyweight""s axis of rotation.) U.S. Pat. No. 5,795,255 to Hooper effects adjustability of COM along the arm of a conventional flyweight by changing the mass within a cavity extending longitudinally through the arm. (Longitudinally means essentially at right angle to the flyweight""s axis of rotation.) The prior art has resulted in near optimum transfer of power from engine to traction when the vehicle is operated near its top speed.
U.S. Pat. No. 4,826,467 to Reese et al. uses a non-conventional flyweight made up of a pair of arms extending in the same direction that are spaced from each other along the pivot""s axis. One of the arms has a driving lip portion at one end (distant from its COM) that might approximate the function of a cam surface and a drive pin extending from its side that causes the other arm to rotate until the COM of the other arm reaches the reference line (where the torque on the other arm becomes zero). Plumb line as used herein was defined previously in terms of a conventional flyweight. However, if one were to drop a plumb line from the center of the Reese pivot while the two arms of Reese are statically suspended by the pivot and free to rotate about the pivot, then one would see that the net COM moves only in the third quadrant even when one arm stops rotating. Reese teaches the use of two spaced arms so as to effect only initially a relatively large arm mass and thereby provide xe2x80x9ca much more rapid response to an increased torque requirement at high speeds.xe2x80x9d
The present invention is directed to improving the performance of CVTs for shift ratios larger than about N:1 where Nxe2x89xa71, while preserving performance for smaller shift ratios. Experimentally, it has been found that enhanced performance for smaller shift ratios can also be effected. Especially for larger shift ratios, a significant problem of the prior art has been slipping of the belt because of insufficient primary pulley side force on the belt. The prior art type of flyweight effects too little side force at lower vehicle speeds and higher shift ratios. Such insufficiency of side force reduces belt life, wastes fuel, and reduces the performance of the vehicle using a CVT. The preferred embodiment, and alternate embodiments, of the present invention go a long way towards correcting this deficiency of the prior art using a flyweight of unique shape and construction with the potential of field adjustability.
A set of known conventional flyweights is shown on FIGS. 1A, 1B, and 1C. FIG. 1A shows an old art flyweight 10 made by Yamaha and used in their SR540D. It is shown in the Yamaha SR540D Service Manual, 1st Edition, a publication dated October 1979. FIG. 1A also looks like the flyweight shown on Model SSR440B Snowmobile Parts List, First Edition, a publication that is dated October 1977. The flyweight has an expected pivot 14A, head 15A, arm 16A, arm COM 17A, and cam surface 18A. The flyweight also has multiple holes-for-rivet 19A that are each adapted to receive one of a set of rivets so as to effect a mass change and COM change. The use of rivets is discussed in the aforementioned Yamaha Service Manual on page 4-4. In operation, cam surface 18A engages a movable roller 50. Also shown on FIG. 1A are reference line 52 and rotational axis 58.
FIG. 1B shows an old art flyweight 10 made by Kawasaki shown in a publication with a title page saying: Clutch Tuning Handbook by Olav Aaen B.S.M.E., M.S.I.A. and with a copyright notice by Aaen Performance Parts Inc., 1979. It is believed that this publication is the predecessor, or the first edition, of the now standard publication Olav Aaen""s Clutch Tuning Handbook, which is now at least available in a 1997 edition. The flyweight has an expected pivot 14B, symmetrical head 15B, arm 16B, arm COM 17B, and cam surface 18B. The flyweight also has at least one hole-for-bolt-and-washer 19B adapted to receive a bolt and washer so as to effect a mass change and COM change. The aforementioned 1979 publication, on page 38, indicates that at least four different flyweights with different masses were available for use, that one nut was used, that two different washers with different masses were available for use, that five different bolts of different masses were available for use, and the provided drawing suggests that bolts and washers can be changed while the flyweights are pivotally mounted. In operation, cam surface 18B engages a movable roller 50. FIG. 1B also shows reference line 52 and rotational axis 58.
The essence of old art flyweight 10 (of FIG. 1B) is believed still to have been in use some years latter from the description found on page 58 of the 1995 edition of Olav Aaen""s Clutch Tuning Handbook, as follows: xe2x80x9cYamaha also has a special flyweight for racing, where additional tuning washers can be screwed on the bottom of the weight with a bolt.xe2x80x9d The art of bolting washers to parts of the arm of a flyweight is old.
FIG. 1C shows an old art flyweight 10, made by Ski-Doo for a 1999 MXZX snowmobile with part number 417-0038-01, that appears different, but merely has the elements rearranged. Pivot 14C is at one end of arm 16C with arm-roller 13C at the other end. Pivot 14C is surrounded by head 15C. In operation, cam surface 18C is fixed and is engaged by the moveable arm-roller 13C. Also shown on FIG. 1C are arm COM 17C, reference line 52, and rotational axis 58.
A 1981 SAE paper by David J. Bents (810103) contains efficiency data on CVTs that could be, and was, reformulated to yield the expected near optimum side forces on the driven pulley of a CVT as a function of shift ratio. Optimum, in this case, refers to minimum power being lost in the transfer of power from the engine to traction. The 1981 SAE paper presents measured data of the required axial force (side force needed just to keep the belt from slipping and thus produce the side force that optimizes efficiency of power transmission) as a function of centerline force (force between the hubs of the two pulleys). A family of such curves is presented for both the driven and driver pulleys, and for various shift ratios. Only the information for the drive (primary) pulley/clutch is used here. Once one knows the actual spacing between the two pulleys and the length of the actual belt, one can reformulate the data presented in the SAE paper in terms of the size of the required axial force as a function of the shift ratios used in the SAE paper. The reformulated data indicates that the ideal side force on the primary pulley decreases monotonically, and essentially linearly, with decreasing shift ratio. Clearly, it would be very difficult, if not impossible, to start an engine while it is connected to an ideal clutch system. One could interpose a disk type clutch (similar to that long used in automobiles) or the like between the engine and the ideal clutch system, disconnect the engine from the ideal clutch system while starting the engine, and then engage the disk clutch. The added complexity, wear, and expense of such a scheme seems undesirable. It is then apparent that the ideal operational relationship between side force and shift ratio is one that starts with a modest side force at the highest shift ratio, increases rapidly to a maximum, and then decreases monotonically with decreasing shift ratio. It is an objective of the present invention to provide a way to produce a close approximation to the ideal operational relationship between side force and shift ratio.
It is an objective of the present invention to effect an improved and near optimum side force that minimizes losses in CVT power transmission systems. It is an objective to effect such a near optimum side force over the full range of shift ratios.
It is a further objective of the present invention to provide a system allowing the tailoring of side force versus shift ratio so as to be close to optimum for a particular CVT. It is an objective for such a system not to need to change the mass of the flyweights while tailoring the system. It is an objective for such a system also to provide a way to adjust flyweight moment-of-inertia while tailoring. Alternatively, it is an objective for such a system to change both the mass and the mass distribution of flyweights while tailoring.
It is a further objective of the present invention to provide an improved system able to be retrofitted to existing CVTs with ease.
The foregoing and other objectives and advantages are achieved with the apparatus and process disclosed below.
The preferred embodiment of the present invention improves conventional flyweights (see examples on FIGS. 1A, 1B, and 1C) by integrally forming thereto a massive shoulder (see FIG. 2A) just beyond the head of a conventional flyweight. The preferred shoulder is a mass concentration (i.e. massive) with a COM located more than 10 millimeters from the pivot center and that is positioned within a 60 degree wide sector centered at the pivot""s center and extending from 60 degrees from the plumb line to 120 degrees from the plumb line. Preferably, the shoulder""s COM is located approximately at right angles to the reference line. FIGS. 2A, 3, and 4 show the preferred embodiment.
The present invention encompasses adding one or more mass concentrations to a conventional flyweight in locations in addition to, or different from, those of the preferred embodiment. The COM of each mass addition or supplement of the present invention is located at least a small distance from the surface of the associated conventional flyweight. xe2x80x9cAdding,xe2x80x9d or xe2x80x9csupplementingxe2x80x9d includes attaching and/or integrally forming the supplemental mass or masses.
At rest, a flyweight imposes no force on the roller because no centrifugal force is produced at rest. To enable the engine to start under only a small load, a compression spring furnishes an appropriate, negligible belt side force such that the belt is essentially decoupled during starting. Just after starting, the arm""s COM is close to the reference line and between the pivot and rotational axis, thus most of the centrifugal force is into the pivot rather than against the roller (which would have ultimately produced belt side force). Just after starting, the preferred embodiment""s shoulder""s COM is farther from the rotational axis than the arm""s COM and thus its centrifugal force term has a larger radius portion, and, since the shoulder""s COM is approximately at right angles to the reference line, the shoulder will produce a significant force against the roller greatly enhancing the belt side force over what would result without the shoulder.
In summery, for the preferred embodiment of the present invention, as shift ratio decreases (vehicles""s speed increases):
(1) the torque from the arm""s COM increases (increasing the force on the roller that tends to increase the belt side force);
(2) the torque from the shoulder""s COM decreases (to zero when the shoulder""s COM is on the reference line) and further decreases in shift ratio beyond the point where the shoulder""s COM is on the reference line (further rotation of flyweight) will cause the shoulder""s COM to subtract torque from that produced by the arm""s COM; and
(3) the sheaves of the primary pulley will become closer together causing the opposing force due to the compression spring to increase.
The desired resultant effect of the preferred embodiment of the present invention is to have a side force component due just to the use of the preferred embodiment that decreases with increased vehicle speed (decreased shift ratio) while the net side force increases rapidly to a peak and then more slowly decreases with decreasing shift ratio (increasing vehicle speed). The shoulder of the preferred embodiment of the present invention causes a desirable large starting torque (proportional to side force) that gets smaller with increasing vehicle speed (even possibly subtracting torque) and the spring also tends to reduces side force as the vehicle speed increases (since the spring is increasingly compressed as the shift ratio decreases). Net side force as a function of shift ratio produced by the preferred embodiment of the present invention is desirable and different from the prior art.
FIGS. 2B and 2C show alternate embodiments of the preferred embodiment that are provided with structure that facilitates adjustment. FIG. 2B shows at least one arm-hole 39 that could receive a rivet or bolt and washer (in the manner of the Yamaha flyweight shown on FIG. 1A or in the manner of the Kawasaki flyweight shown on FIG. 1B) and an axial shoulder-hole 32 in shoulder 31 that may be used to attach mass to shoulder 31. FIG. 2C shows at least one arm-hole 49 that could receive a rivet or bolt and washer (in the manner of the Yamaha flyweight shown on FIG. 1A or in the manner of the Kawasaki flyweight shown on FIG. 1B) and a longitudinal shoulder extension 42 in shoulder 41 that may be used to attach mass to shoulder 41.
An additional embodiment is shown on FIG. 2D. The alternate-flyweight 70 includes shoulder-piece 71 and arm-piece 76 having cam surface 78. Shoulder-piece 71 and arm-piece 76 overlay each other such that the two rotate as one until shoulder-piece 71 touches obstruction 80. Thereafter, arm-piece 76 may continue to rotate while shoulder-piece 71 ceases rotation.
A further embodiment is shown on FIGS. 2E1 and 2E2 as flyweight 90. In this embodiment, shoulder 21 of the preferred embodiment is replaced by massive toggle shoulder 91 that is attached to head 95 with secondary pivot 92. Flyweight 90 as a whole revolves about pivot 94 while toggle shoulder 91 toggles between at least two positions.
FIG. 2F shows the manner that the present invention would use to place the preferred massive shoulder on head 15C to effect Ski-Doo shoulder 11C.